[T]here’s one permutation that absolutely, no question about it, would destroy the rest of Barack Obama’s presidency is: a disastrous war. Ask Lyndon Johnson or George W. Bush. Or Harry Truman. Unending, seemingly pointless wars are the one sure way to ruin a presidency.

Now, I’m not saying that’s in the cards; in fact, I don’t think it is. I’m just saying: that’s the kind of thing that really does matter a lot to presidencies. And if you do believe that the administration is going down a path that winds up there, or a path that has a high risk of winding up there, then you should be very worried about the health of this presidency.

If not? None of the other permutations here are anywhere close to that kind of threat to the Obama presidency. Presidents lose key votes which are then mostly forgotten all the time. They pursue policies which poll badly, but are then mostly forgotten, all the time. There are important things to say about all of that, because “mostly” isn’t completely. But the first thing to get right when considering the effects of Syria policy on the rest of the Obama presidency is that the scale of a Vietnam or an Iraq (or a Korea, for that matter) overwhelms everything else we might talk about.

When it comes to Syria commentary, there are plenty of foxes tearing each other to pieces. But Bernstein has recalled us to a crucial piece of hedgehog wisdom. Big, endlessly escalating, unwinnable wars not only kill people (something Serious People not supposed to think about). More to the pundit’s point, they kill presidencies.